NEWS FROM SPACE

TWO CLUSTERS SUGGEST STAR BIRTH SCENARIO
IN THE EARLY UNIVERSE

Hubble Telescope observations of a pair of star clusters have provided
new insights into how stars might have formed many billions of years ago
in the early universe. The pair of clusters are 166,000 light-years away
in the Large Magellanic Cloud (LMC) in the southern constellation
Doradus. The clusters are unusually close together for being distinct
and separate objects according to Hubble astronomers.

Previously, such detailed stellar population studies were restricted to
nearby star-forming regions within the plane of our Milky Way Galaxy.
However, Hubble's high-quality images extend these stellar studies one
hundred times farther into the universe, out to the distance of a
neighboring galaxy. Because the LMC lies outside of our Milky Way
Galaxy, it is a natural laboratory for studying the birth and evolution
of stars. The stars in the LMC have few heavy elements, thus their
composition is more primordial--like the stars that first formed in the
early universe.

A preliminary assessment of the HST observations indicates that these
compact clusters contained many more massive stars than expected. "If
this were also the case billions of years ago, it would have altered
drastically the early history of the universe," says Dr. Nino Panagia of
the Space Telescope Science Institute and the European Space Agency.

Panagia and R. Gilmozzi (also of STScI/ESA) and co-investigators
utilized HST's unique capabilities--ultraviolet sensitivity, ability to
see faint stars, and high resolution--to identify three separate
populations in this concentration of nearly 10,000 stars. Previous
observations with groundbased telescopes resolved less than 1000 stars
in this region. About 60% of the stars belong to the dense cluster
called NGC 1850, which is estimated to be 50 million years old. A loose
distribution of extremely hot massive stars in the same region are only
about 4 million years old and represent about 20% of the stars in the
image. (The remainder are field stars in the LMC.) The significant
difference between the two cluster ages suggests these are two separate
star groups that lie along the same line of sight. The younger, more
open cluster probably lies 200 light-years beyond the older cluster,
says Panagia. He emphasizes that if it were in the foreground, then dust
in the younger cluster would obscure stars in the older cluster.

Because having two well-defined star populations separated by such a
small gap of space is unusual, this juxtaposition suggests that they
might be linked in an evolutionary sense. A possible scenario is that an
expanding "bubble" of hot gas, from more than 1000 supernova explosions
in the older cluster, might have triggered the birth of the younger
cluster. This would have happened when the bubble expanded across space
for 45 million years before plowing into a wall of cool gas and dust.
The shock front then caused the gas to contract, precipitating a new
episode of star formation. The massive, hot stars are destined to
explode in a few million years, and thus create yet a new expanding
bubble of gas.

This composite image is assembled from exposures taken in ultraviolet,
visible, and near-infrared light. Yellow stars correspond to Main
Sequence stars (like our Sun) with average surface temperatures of 6000
Kelvin; red stars are cool giants and supergiants (3500 K); white stars
are hot young stars (25,000 K or more) that are bright in
ultraviolet.

IDA'S MOON NAMED DACTYL

The International Astronomical Union (IAU) has approved the name Dactyl
for the tiny moon discovered this year in orbit around the asteroid Ida
by the Galileo spacecraft. The IAU also approved names for surface
features on the asteroid Gaspra, which became the first asteroid ever
visited by a spacecraft when Galileo flew by it on October 29, 1991.

Dactyl is the first natural satellite of an asteroid ever discovered and
photographed. The tiny moon, about one mile (1.5 kilometers) across, was
discovered in images returned by Galileo after its flyby of the asteroid
on August 28, 1993. The discovery was confirmed in March 1994 by members
of Galileo's imaging and infrared science teams who recommended the new
name to the IAU, which is responsible for the formal naming of solar
system bodies.

The name is derived from the Dactyli, a group of mythological beings who
lived on Mount Ida, where the infant Zeus was hidden--and raised, in
some accounts--by the nymph Ida and protected by the Dactyli. Other
mythological accounts say that the Dactyli were Ida's children by
Zeus.

Three regions on Gaspra were named for scientists associated with the
asteroid. Neujmin Regio was named for G. Neujmin, the Ukrainian
astronomer who discovered the asteroid in 1916. Yeates Regio honors the
late Dr. Clayne M. Yeates, who was Galileo Science Manager and Science
and Mission Design Manager until his death in 1991. Dunne Regio was
named in honor of the late Dr. James A. Dunne, who served as Galileo
Science and Mission Design Manager until late 1992.

Galileo continues on its way to Jupiter where it will send a probe into
the atmosphere on December 7, 1995, and then go into orbit for a two-
year scientific tour of the planet, its satellites, and its
magnetosphere.

Fullerenes found in samples from Sudbury impact Structure

Fullerenes thought to be of extraterrestrial origin have been found in
shock-produced impact breccias at the Sudbury impact structure in
Ontario, Canada, by researchers at Scripps Institution of Oceanography,
Argonne National Laboratories, and NASA Ames Research Center.

The huge crater, formed almost two billion years ago by an asteroid or
comet and strongly deformed by subsequent geological activity, contains
the largest deposit of natural fullerenes found on Earth to date. "For
the first time, we can point to carbon in an impact crater and say that
it is probably extraterrestrial," Theodore Bunch, a NASA Ames Research
Center scientist said. Fullerenes, usually made of 60 carbon atoms
(sometimes 70) arranged like a soccer ball-shaped cage, are the rarest
form of elemental carbon that occurs naturally on Earth. Diamond and
graphite are other, more common, forms.

Bunch collected rock samples from three sites in the crater, which is
110 miles (164 kilometers) in diameter. Laser analysis was performed by
Luann Becker at the Argonne National Laboratories. Bunch said the
molecules, also known as buckyballs, probably formed during the impact
event by cannibalizing other carbon forms or organic compounds contained
in the comet.

According to Bunch, heat from the impact may also have stripped carbon
from the abundant carbon dioxide scientists think saturated Earth's
early atmosphere. The object was a comet rather than an asteroid, Bunch
suggests, because of the large amounts of carbon found in the impact
deposits. He estimates that the comet was 10 miles (15 kilometers) in
diameter and contained 20-30% carbon.

The fullerenes in rock samples from the Sudbury impact site range
between 1 and 10 parts per million. The abundance of sedimentary carbon
in the Sudbury impact target rocks is less than 1%, an insignificant
carbon source for the fullerenes. "The startling thing is that not only
were the fullerenes there, but they were there in an amount that is
really extraordinary," said Jeff Bada, a professor at Scripps
Institution of Oceanography.

Bunch, with another research team, recently found fullerenes in a tiny
crater on the Long Duration Exposure Facility (LDEF) spacecraft that had
orbited Earth for almost six years. It is unclear whether the fullerenes
came from a carboneaceous micrometeorite or were formed by the high-
speed collision creating the crater.

The large ball-shaped carbon molecules are thought to form in red giant
or carbon stars that are nearing the end of their stellar lives. They
were discovered in 1985 on Earth by accident when scientists heated
carbon vapor to temperatures exceeding 14,000 degrees Farenheit.

The first naturally occurring fullerenes on Earth were found in July,
1992, in carbon-rich rock in ancient sediments in Russia. They have also
been found in Colorado, formed in melted rock where vegetation (carbon)
was present when lightning struck the ground. But the amounts previously
detected on Earth are much smaller than those discovered at the Sudbury
site.

The Sudbury structure is the second largest impact crater on Earth. Only
the Chicxulub crater, formed by the 65-million-year-old impact that led
to mass extinctions including the dinosaurs, is larger. Fullerenes
associated with Chicxulub could have come from the impactor itself or
have been formed in the intense global forest fires ignited by the
explosion.

A similar process, Bunch said, may have happened during Comet Shoemaker-
Levy's fiery plunge into Jupiter's stratosphere, burning carbon
compounds in the jovian atmosphere. Carbon freed from the jovian
atmosphere (and the comet) could have combined into soot and possibly
some fullerenes, he said, forming the mysterious dark spots visible
after the impacts.

HUBBLE TRACKS ROTATION OF URANUS

New Hubble Space Telescope images of Uranus reveal the motion of a pair
of bright clouds in the planet's southern hemisphere and a high altitude
haze that forms a cap above the planet's south pole.

The images were obtained on August 14, 1994, when Uranus was 1.7 billion
miles (2.8 billion kilometers) from Earth. Atmospheric details have been
seen before only by the Voyager 2 flyby in 1986. Since then, detailed
observations of Uranus's atmospheric features have not been possible
because the planet is at the resolution limit of groundbased
telescopes.

Hubble's Wide Field Planetary Camera 2 observed Uranus through a filter
that is sensitive to light reflected by high altitude clouds. This
allows us to see a high-altitude haze over Uranus' south polar region,
along with the pair of high-altitude clouds or plume-type features, 2500
and 1800 miles (4300 and 3100 kilometers) across, respectively. The
sequence of images shows how the clouds (labeled A and B) rotate with
the planet during the three hours that elapsed between the first two
observations (left and center) and the five hours that elapsed between
the second pair (center and right). Some cloud motion might be due to
high-altitude winds on the planet.

By tracking the motion of high-altitude clouds, astronomers can make new
measurements of Uranus' rotation period. Based on Voyager observations,
Uranus is thought to complete one rotation every 7 hours, 14 minutes.
One of the four gas giant planets of our solar system, Uranus appears
largely featureless. Unlike other planets, its south pole points toward
the Sun during part of the planet's 84-year orbit.

Credit: Kenneth Seidelmann, U.S. Naval Observatory, and
NASA

TWO KINDS OF COMETARY ICE?

Slight temperature differences in the two comet-forming regions of the
solar system cause the water ice that largely makes up comets to form in
different ways, researchers from NASA's Ames Research Center say. "We
predict that comets from the Kuiper belt and Oort cloud contain
structurally different forms of water ice," Peter Jenniskens said.
Jenniskens, with David Blake, published their results in the August 5
issue of Science.

Comets are thought to be pristine chunks of debris left over from the
solar system's formation about 5 billion years ago. They are made of
more than 40% water ice and come from exceedingly cold regions of the
solar system. According to Jenniskens, two populations of comets exist,
based on their present location in the solar system and where scientists
think they originated.

Some comets formed in the Kuiper belt, which is in the outer region of
the solar system beyond Pluto's orbit. These comets, known as short-
period comets, probably formed at temperatures colder than -370 F, he
said. Oort cloud comets probably formed in the Neptune-Uranus region and
were then expelled to much greater distances from the Sun. Oort cloud
comets, known as long-period comets, were probably formed at
temperatures warmer than -320 F, Jenniskens said.

Most Oort cloud comets come from a solar "sphere" around 30,000
astronomical units (AU) away, but scientists think the cloud itself
extends almost halfway to the nearest star, Alpha Centauri, which is
four light-years from the Sun. One AU equals the distance from the Earth
to the Sun. There are about 60,000 AU in a light year.

Water vapor frozen onto the rocky grains which coalesced to form comets
is frozen like a glassy film rather than a crystalline solid, Jenniskens
said. This glassy ice has the same basic structure as liquid water. In
this form, the water molecules are connected to each other by four
strong hydrogen bonds in an open cage-like structure. At the very low
temperatures of comet formation in the Kuiper belt_colder than -380 F--
some water molecules are trapped in the cages of this structure during
freezing. But comets formed at slightly higher temperatures in the Oort
cloud expelled the water from the cages. Kuiper belt comets, therefore,
consist of a different form of water ice than Oort cloud comets.

Comet Shoemaker-Levy, which recently crashed into Jupiter, was most
likely a lower-temperature, short-period comet formed in the Kuiper
belt, Jenniskens said. Because short-period comets orbit the solar
system faster and more often, Jupiter's gravity is more likely to
capture them, he said.

These predictions are based on laboratory simulations of cometary ice
formation under conditions thought to exist when the objects formed. The
researchers discovered the water-trapping process of the lower
temperature comets by simulating the freezing process in an Ames
laboratory and observing with a transmission electron microscope.

MAGELLAN'S LEGACY: REVEALING THE FACE OF
VENUS

The Magellan mission to Venus ended on October 12 as Earth-based
tracking stations lost the spacecraft's radio signal at 10:02 Universal
Time (3:02 a.m. PDT). The loss of signal, which had been expected, was
caused by low power on the spacecraft exacerbated by Magellan's
orientation as it performed a final experiment in the upper atmosphere.
Magellan was expected to burn up in the planet's upper atmosphere within
two days.

The spacecraft's thrusters were fired in four sequences on October 11 to
lower its orbit into the thin upper atmosphere and set up the final
experiment. Magellan gathered scientific data on the upper atmosphere
and spacecraft aerodynamics during the final descent by orienting its
solar panels in opposite directions like a windmill. The termination
experiment was an extension of the windmill experiment performed in
early September. It was carried out as the spacecraft was within weeks
to days of the end of its life because of degradation of solar power
output by the thermal stress of more than 15,000 orbits of Venus.

Launched in May 1989, Magellan entered Venus orbit in August 1990 and
gathered data for over four years. It used radar to see through clouds
enshrouding the planet to map 98% percent of the surface with an average
resolution of better than 300 meters and compiled a high-resolution
gravity field map for 95% of the planet. The gravity data will allow
scientists to develop models for the planet's interior and evaluate them
in light of surface features revealed by Magellan's radar imaging.

Magellan also performed the first aerobraking maneuver by dipping into
the atmosphere to reshape its orbit. This technique is being used in
designing the Mars Global Surveyor mission, enabling the spacecraft to
enter Mars orbit in 1997 using less fuel, thus saving weight and
cost.

"The Magellan mission to Venus has been successful beyond all
expectations," said JPL Director Edward Stone. "It not only fulfilled
its science and mission objectives, it also demonstrated innovative
technologies for future missions."